Scale text - iOS

On iOS, you can use Dynamic Type to scale text. By using this function, the font size is adjusted to the preferences of the user. If you're using your own font, you can use the scaledFont method from UIFontMetrics to calculate the font size.

Text elements such as UILabel, UITextField and UITextView have a property called adjustsFontForContentSizeCategory. If you set it to true, the element automatically updates its font when the device's content size category changes.

For adjustsFontForContentSizeCategory to take effect, the element’s font must be one of the following:

• A font vended using preferredFont(forTextStyle:) or preferredFont(forTextStyle:compatibleWith:) with a valid UIFont.TextStyle
• A font vended using UIFontMetrics.scaledFont(for:) or one of its variants

// MARK: - Scaling custom fonts
import UIKit

extension UIFont {

    static func font(name: String, size: CGFloat, style: TextStyle) -> UIFont {
        guard let font = UIFont(name: name, size: size) else {
            fatalError("Font \(name) does not exist")
        }
        return UIFontMetrics(forTextStyle: style).scaledFont(for: font)
    }
    
    static func openSans(weight: UIFont.Weight, size: CGFloat, style: TextStyle) -> UIFont {
        if UIAccessibility.isBoldTextEnabled {
            return font(name: "OpenSans-Bold", size: size, style: style)
        }
        
        switch weight {
            case .regular:
                return font(name: "OpenSans-Regular", size: size, style: style)
            case .semibold:
                return font(name: "OpenSans-SemiBold", size: size, style: style)
            case .bold:
                return font(name: "OpenSans-Bold", size: size, style: style)
            default:
                fatalError("Font weight \(weight) is not supported")
        }
    }
}

// MARK: - Enabling content size category adjustments
label.adjustsFontForContentSizeCategory = true